A facile approach to preparation of long-chain-branched poly(p-dioxanone)
A facile approach to preparation of long-chain-branched poly(p -dioxanone)
Feng Chen a ,Si-Chong Chen a,*,Ke-Ke Yang a,b ,Xiu-Li Wang a ,Yu-Zhong Wang a,b,*
a Center for Degradable and Flame-Retardant Polymeric Materials (ERCEPM-MoE),College of Chemistry,Sichuan University,Chengdu 610064,China b
State Key Laboratory of Polymer Materials Engineering,Sichuan University,Chengdu 610064,China
a r t i c l e i n f o Article history:
Received 4April 2009
Received in revised form 31July 2009Accepted 9September 2009
Available online 12September 2009Keywords:
Long-chain-branch Poly(p -dioxanone)Chain-extending Rheology
a b s t r a c t
Long-chain-branched poly(p -dioxanone)s (LCB-PPDOs)with different branch densities were prepared via the chain-extending reaction of hydroxyl group terminated linear bi-functional PPDO (2a-PPDO)and star-like tri-functional PPDO (3a-PPDO)prepolymers,which were synthesized by the ring-opening polymerization of p -dioxanone (PDO)using 1,4-butanediol (BD)and trimethylolpropane (TMP)as multi-functional initiators,respec-tively.The undesirable gelation was successfully depressed by adjusting the chain length and feed ratio of prepolymers.The average molecular weight between branch points (M b )and the average number of branch per 100,000g/mol (B n )of LCB-PPDOs were calcu-lated from the 1H NMR spectra.The average number of branch ranged from 0to 6.72branch points per 100,000g/mol,and the number-average molecular weights between branch points ranged from 6900to 20,500g/mol.The results of differential scanning calo-rimetry (DSC)showed that the crystallization behavior of LCB-PPDOs was changed evi-dently with the branch density.Small-amplitude dynamic oscillatory rheometer was used to investigate the rheological properties of the melts of LCB-PPDO including zero-shear viscosity,storage modulus,relaxation times and loss angle,which largely depended on the branch density and length of LCB-PPDOs.Therefore,the rheological behaviors of PPDO can be well-controlled via synthesizing LCB-PPDOs with the desired architectures.
ó2009Elsevier Ltd.All rights reserved.
1.Introduction
As a biodegradable polyether ester,poly(p -dioxanone)(PPDO)has attracted many attentions because of its special characters.The coexistence of ester and ether bonds in poly-mer chains endues PPDO with both excellent biodegradabil-ity and ?exibility [1].Compared to other well reported biodegradable aliphatic polyesters,such as polylactic acid (PLA),polycaprolactone (PCL),poly(b -hydroxybutyrate)(PHB),PPDO not only have good mechanical strength (ten-sile strength >30MPa),but also have excellent ?exibility (elongation at break >300%)and proper melting tempera-ture (110°C).The PPDO has already been used in some bio-medical applications such as suture,bone repair device and may have potential applications in peroral or parenteral
drug delivery systems.With the decrease of its monomer cost,PPDO also may be used in universal uses,such as ?lms,molded products,laminates,foams,non-woven material,adhesives and coatings [1–3].However,the linear PPDO,which has relatively low melt strength,is very hard to ther-moform in common thermoplastic processing,especially foaming and blow molding.
Introducing long-chain branches to linear polymer is an effective approach to increase the melt strength [4–6].A long-chain-branch (LCB)is long enough to entangle with other chains in melt and concentrated solutions,thereby altering the ?ow properties.The LCB polymers were found to exhibit the following properties:lower Newtonian viscos-ity and stronger shear thinning than a linear polymer of equal molecular weight,strong melt elasticity expressed by the ?rst normal stress difference and storage modulus,and enhanced strain hardening under elongational ?ow [7,8].Various types of branched polyesters such as star-branched,comb-like,randomly branched and super-branched
0014-3057/$-see front matter ó2009Elsevier Ltd.All rights reserved.doi:10.1016/j.eurpolymj.2009.09.008
*Corresponding authors.
E-mail addresses:chensichong@https://www.wendangku.net/doc/7e8568447.html, (S.-C.Chen),yzwang@https://www.wendangku.net/doc/7e8568447.html, (Y.-Z.Wang).
European Polymer Journal 46(2010)24–33
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polyesters,were prepared using different polymerization techniques[4,9–12].The strategies of preparation of these LCB-polyesters were based on the co-polycondensation of multi-functional(>2)monomer with bi-functional mono-mer.Hess et al.[11]changed the level of random branching in PET by adding different levels of trimethylolpropane (TMP)to the melt polymerization,and the branched PET possessed a lower zero-shear viscosity compared to linear chains of equal M w.Kim et al.[12]prepared long branched polybutylene succinate(PBS)by introducing a branching agent,trimethylol propane(TMP),to the polycondensation system of succinic acid and1,4-butanediol,and observed an increased shear-thinning extent and decreased loss tangent as the level of tri-functional branching agent was increased. For those polyesters,such as PET and PBS,prepared by poly-condensation reactions,the LCB structure is relatively easy to obtain by introducing a certain amount of multi-functional monomer.
However,to the best of our knowledge,no attempt about the preparation of those LCB-aliphatic polyesters ob-tained by ring-opening polymerization of lactone or lac-tide,such as PCL,PLA and PPDO,was reported,probably because it was very hard to obtain the multi-functional cyclic monomer for ring-opening polymerization.
The aim of this work is to synthesize long-chain-branched poly(p-dioxanone)(LCB-PPDO)so as to improve the rheological and processing properties of PPDO.A relatively facile synthesis strategy was adopted to prepare LCB-PPDO.Firstly,trimethylolpropane(TMP)was used as initiator and SnOct2as a catalyst to initiate the ring-opening polymerization of PDO,given the star-shaped tri-hydroxyl-terminated poly(p-dioxanone)(3a-PPDO) prepolymer[13].Then LCB-PPDOs with different branch density were synthesized via the reaction between the ter-minated hydroxyl groups of prepolymer using hexameth-ylene diisocyanate(HDI)as the chain-extending agent, which has the low toxicity of its degradation products and high reactive activation for–OH groups[14].Com-pared to those traditional methods preparing branched polyesters,the coupling reaction of functional terminated prepolymer could produce LCB polymer with relatively short time and high ef?ciency.Moreover,the molecular structure of LCB polymer could also be easily controlled by adjusting the chain length of prepolymers.To depress the probability of gelation,linear bi-hydroxyl-terminated PPDO prepolymer was introduced to the chain-extending reaction.The in?uence of the molecular topology on the rheological and crystallization behaviors of the LCB-PPDOs was discussed.
2.Experimental
2.1.Materials
The monomer of PPDO,p-dioxanone,was provided by the Pilot Plant of the Center for Degradable and Flame-Retardant Polymeric Materials(Chengdu,China)and puri?ed by vacuum distillation from CaH2.SnOct2was pur-chased from Sigma Aldrich(USA)and used as received.1,4-Butanediol(BD)was purchased from Zhiyuan Chemical Company(Tianjin,China)and used after vacuum distilla-tion for three times.Trimethylolpropane(TMP)was pur-chased from Sinopharm Chemical Reagent Co,Ltd.and used without further puri?cation.Hexamethylene diisocy-anate(HDI)was purchased from Tokyo Chemical Industry Co.and used without further puri?cation.
2.2.Preparation of2a-PPDO prepolymer and3a-PPDO prepolymer
The polymerization of PDO was performed in a?ame-dried and argon-purged glass reactor with magnetic stir-ring.Firstly,a certain amount of TMP was put into different reactors,into which BD was injected with a syringe.Then, the PDO monomer was injected into the reactors after re-peated evacuation and purging with argon several times, and the reactors were immersed into an oil bath at80°C with stirring for30min.The polymerization was conducted for48h after certain amount of the SnOct2/toluene solution was injected into the reactors.The reactors were rapidly cooled to room temperature via ice cooling after reaction and the product was shattered with crushing machine.
2.3.Preparation of LCB-PPDO via chain extending
Scheme1illustrates the reaction mechanism of forming LCB-PPDO polymers via the reaction between the termi-nated hydroxyl group of prepolymers and NCO group of HDI.In this work,three pairs of the prepolymers with dif-ferent lengths of chains were used(Table1).3a-PPDO pre-polymer(10g)and2a-PPDO prepolymer(10g)were put into a dried glass reactor.The reactor was rigorously dried by evacuating and purging with argon several times prior to immerse into a temperature-adjusted silicone oil bath. HDI was injected with a syringe while stirring after the prepolymers were melted completely and commixed uni-formity.The reaction was allowed to proceed for1h under argon until the intrinsic viscosity were not raised and then rapidly cooled to room temperature via ice cooling after reaction.The crude products were grinding milled to pow-der and then soxhlet-extracted by using aceton(containing 1%of ethanol)as solvent for more than48h,followed by drying in50°C vacuum oven until constant
weight
Scheme1.Synthesis of LCB-PPDO.
F.Chen et al./European Polymer Journal46(2010)24–3325
reached.The unreacted–NCO groups were then removed or terminated before the characterization.
2.4.Characterization and test
The number-average molecular weight(M n)and molec-ular weight distribution(MWD,M w/M n)of prepolymers were determined by gel permeation chromatography (GPC)(Waters1515isocratic HPLC pump,Waters717plus autosampler,Waters2414refractive index detector)at 30°C with a calibration curve constructed using polysty-rene(PSt)standards.Chloroform was used as solvent and eluent with a?ow rate of1.0mL/min.The intrinsic viscos-ity[g]was measured in phenol/1,1,2,2-tetrachloroethane (1:1v/v)solution using an Ubbelohde viscometer main-tained at30°C.1H NMR spectra(400MHz)and13C NMR spectra(100MHz)were recorded by a Varian Inova400 NMR Spectrometer using deuterated chloroform(CDCl3) for prepolymer and deuterated dimethyl sulfoxide(d6-DMSO)for LCB-PPDO as solvent.All the samples were packed with?lter paper and then Soxhlet extracted in boil-ing acetone for48h before test.DSC measurement was per-formed with TA Q200(TA instruments,USA)in sealed aluminum pan under nitrogen atmosphere.The samples were cooled toà50°C from room temperature,and then heated to140°C at a heating rate of10°C/min,kept for 5min to eliminate the thermal history,then cooled to à50°C at a cooling rate of10°C/min.The samples were again heated up to140°C at the same rate.X-ray diffraction patterns were taken on a Philips X’Pert X-ray diffractometer with Cu Ka radiation.Rheological measurements were per-formed on a rotational rheometer,Gemini200HR(Bohlin Instruments,UK)using a heated stream of nitrogen gas for temperature control.All measurements were performed under a nitrogen atmosphere,and25mm parallel plates with gap slightly exceeding1mm were used.Samples were formed into25mm disks by compression-molding.Small-amplitude oscillatory shear was performed in the fre-quency range of0.01–100rad/s at120°C.
3.Results and discussion
3.1.Preparation and characterization of PPDO prepolymers
The prepolymers,hydroxyl-terminated linear bi-func-tional PPDO(2a-PPDO)and star-shaped tri-functional PPDO(3a-PPDO)prepolymers,were prepared by using 1,4-butanediol(BD)and trimethylolpropane(TMP)as an initiator,respectively,and SnOct2as a catalyst.Hydroxyl groups reacted with catalyst,stannous octate(Sn(Oct)2), to co-initiate the ring-opening polymerization of PDO monomer.Therefore,the length of chain can be controlled by changing the molar ratios of PDO/initiator[15].All the samples were prepared at150°C for1h.The molecular characteristics of prepolymers are listed in Table1.The results clearly indicated that the molecular weights in-creased with the feed molar ratio of PDO to initiators.
1H NMR(400MHz,CDCl
3
)was used to learn the detailed information on the microstructure of2a-PPDO and3a-PPDO.Resonances located at d H a4.1ppm,d H b3.8ppm, d H c4.2ppm were assigned to the three methylene hydrogen atoms of PPDO,respectively.The signals occurring at d H h 1.7ppm and d H q4.05ppm were assigned to the methylene protons of BD in2a-PPDO.The signal occurring at d H f 0.88ppm was assigned to the methyl protons of reacted TMP in3a-PPDO.The signals of3a-PPDO at d H g1.5ppm, d H e4.07ppm and d H e’3.45ppm were assigned to the meth-ene groups connected with methyl,ester,and hydroxyl groups,respectively(Fig.1).The resonance at d H e’3.45ppm suggested that the uncompleted esteri?cation of hydroxyl groups of TMP.
The number-average molecular weights of the prepoly-mers derived from different methods were listed in Table 1.It was found that the M n0calculated by NMR was less than theoretical value(M n00)among all the different ratios of PDO/OH,which was caused by unreacted monomer. The M n obtained from GPC measurement was the highest among three different methods.Similar trend was reported for some other aliphatic polyester such as PLLA and PBS [16].
3.2.Synthesis of LCB-PPDOs
The detail approach of synthesis of LCB-PPDO was de-scribed above and outlined in Scheme1.All the samples were prepared at150°C for60min and HDI was used as the chain-extending agent.Since the resulted long-chain branch structure could be controlled by adjusting the molecular weight of prepolymers[17],three pairs of the prepolymers with different chain lengths were used for preparing LCB-PPDO with different molecular structure. Theoretically,the chain-extending reaction of prepolymer
Table1
Preparation condition and the molecular weight of the PPDO prepolymer.
Sample PDO/OH
(mol/mol)OH/SnOct2
(mol/mol)
Yield(%)M n a
(?103g/mol)
M w a
(?103g/mol)
MWD a D p b M0n c
(?103g/mol)
M n00d
(?103g/mol)
2a-2020/1500/185.4 6.38.2 1.3037 3.9 4.3 3a-2020/1500/187.810.414.3 1.3747 5.0 6.3 2a-4040/1500/189.213.318.4 1.39818.38.3 3a-4040/1500/188.916.322.0 1.35909.312.4 2a-6060/1500/189.016.022.1 1.399710.012.3 3a-6060/1500/191.124.334.2 1.4015616.018.5
a Measured by GPC.
b The degree of polymerization of prepolymers,calculated by1H NMR:for2a-PPDO:D
p
=2I b/I d,Ib;for3a-PPDO:D p=3I b/2I f.
c The M0
n was calculated by1H NMR as follows:for2a-PPDO:M0n=D p?102+90;for3a-PPDO:M0n=D p?102+134.
d Th
e M00
n is the theoretical molecular weight of prepolymer calculated by the feed ratio of PDO/initiators.
26 F.Chen et al./European Polymer Journal46(2010)24–33
with tri-functional terminal groups may result in gelation of ?nal products [18].The probability of gelation depends directly on the concentration of the tri-functional terminal groups in the reaction system.Therefore,to avoid the gela-tion by decreasing the concentration of tri-functional ter-minal groups,bi-functional prepolymer 2a-PPDO with different molecular weight and contents were added.The relationship between intrinsic viscosity [g ]of products and the feed ratios of –NCO/–OH were also studied.Although the molecular weight can not be calculated from the data of intrinsic viscosity due to the existence of LCB structure,it was still a good way to compare the magni-tude of molecular weight among them.And the number of terminated hydroxyl groups of prepolymers was equal to the number of hydroxyl groups of initiators.The prod-ucts were dissolved in phenol/1,1,2,2,-tetrachloroethane (1:1/v:v)to determine whether the gelation occurred.The results are presented in Fig.2.
For those prepolymer with high molecular weight,no gelation was observed in the whole range of –NCO/–OH ra-tio.The intrinsic viscosities of LCB-PPDOs increased with the increase of –NCO/–OH ratio ?rstly,but after reached the maximum value,when the –NCO/–OH ratio was slightly higher than the 1:1,the intrinsic viscosity of LCB-40s and LCB-60s decreased with the addition of more HDI.These results are in good accordance with those of re-ported for chain-extending reaction of linear PPDO [15].The excess HDI may act as terminated agent,which
de-
Fig.1.1H NMR spectra of prepolymer of 2a-PPDO (a)and 3a-PPDO (b).
F.Chen et al./European Polymer Journal 46(2010)24–3327
creased the concentration of hydroxyl groups.For branched polymer,not only the molecular weight but also the branch density has important in?uence on the intrinsic viscosity ([g ]).The branched polymer had lower [g ]than the linear polymer with similar molecular weight,and this deviation increased with the branch density [17].In this work,because of the introduction of linear bi-functional prepolymer 2a-PPDO,the branch density of the resulting products was relatively low compared to those of common branched polymer.The increase in [g ]of LCB-PPDO attrib-uted to the increase of molecular weight overwhelm the decrease of [g ]attributed to increase of branch density.Therefore,the [g ]of LCB-PPDO showed similar changing trend as those of chain-extending reaction of linear bi-functional polymers using isocyanate as extender [15].For prepolymer with low molecular weight (2a-20/3a-20),gelation was observed when the HDI/OH ratio higher than 1:1.When more 2a-PPDO was added,the minimum –NCO/–OH ratio at which the gelation occurred also in-creased obviously.This phenomenon was attributed to the changes in concentration of tri-functional terminal hy-droxyl groups.The prepolymer with shorter chain length or higher content of 3a-PPDO have higher concentration of tri-functional terminal hydroxyl groups and therefore have higher probability of gelation.Therefore,it is an effec-tive way to avoid the gelation by adjusting the concentra-tion of tri-functional terminal hydroxyl groups.
3.3.Molecular structure of LCB-PPDO
The 1
H NMR (DMSO,400MHz)spectroscopy of LCB-PPDO was shown in Fig.3(a).Besides the three typical sig-nals ascribed to PPDO units (d H a 4.16ppm,d H b 3.76ppm,d H c 4.21ppm)and the signals ascribed to TMP (d H f 0.88)and BD (d H h 1.68)units,the weak single peaks at 7.18ppm (d H m )and 1.26ppm,1.43ppm,2.98ppm are as-cribed to the amide –NH groups and methylene protons of HDI (Fig.3a),suggesting that the prepolymers were suc-cessfully coupled by HDI.Weak resonances of PDO mono-mer were found in the NMR spectra of LCB-PPDO,suggesting that a trace amount of PDO monomer was formed by the unzipping reaction of PPDO [19]during the chain-extending reaction at 150°C.Since the amount of monomer was relatively small,it did not show obvious impact on the properties of the samples.13C NMR spec-trum of LCB-PPDO was shown in Fig.3(b).The peak at 68.9,72.6,74.4and 175.4ppm are assigned to carbons of methene groups and carbonyl group PPDO,respectively.The resonance of the isocyanate group which typically oc-curred at about 121ppm was not observed,suggested that the unreacted –NCO groups had been reacted or removed after the puri?cation.
The average molecular weight between branch points and the average number of branch per 100,000g/mol (B n )of LCB-PPDO can be calculated from 1H NMR spectra by fol-lowing equations and listed in Table 2.
The intensity of the methyl groups (I 0.88)and methine groups (I 1.67)can be used to calculate the molar ratio (M r )of 3a-PPDO to 2a-PPDO in the products by the follow-ing equation:
M r ?
n 2a n 3a ?
3?I 1:67
4?I 0:88
e1T
where I 1.67is the intensity of methene groups of BD and I 0.88is the intensity of methyl groups of TMP,n 3a and n 2a are the average numbers of 3a-PPDO and 2a-PPDO seg-ments per LCB-PPDO molecule,respectively.
The average molecular weight between branch points (M b )can be expressed by following:
M b ?
2
3
?M 3a tM r ?M 2a e2T
where M 3a and M 2a are the number-average molecular weights of 3a-PPDO and of 2a-PPDO,respectively.
The average number of branch per 100,000g/mol (B n )can be calculated by following equation [1]:
B n ?
100;000M b
à1
2
e3T
A series of LCB-PPDOs with similar molecular weight but different branch densities were selected for investigating the in?uence of molecular structure on the characteristics of LCB-PPDO.The factors of molecular structure,such as the average number of branch per 100,000g/mol (
B n ),the average molecular weight between branch points,which derived from the equations hereinbefore,of those LCB-PPDOs are all listed in Table 2.
3.4.Thermal and crystalline behaviors of LCB-PPDO polymers
The thermal behavior and crystallization of LCB-PPDO were studied via DSC.Clearly,the LCB structures include M b and branch density does have a signi?cant in?uence on the thermal behavior and the crystallinity.The DSC curves of LCB-PPDOs and linear PPDO during the ?rst heat-ing scan and cooling scan and the subsequent reheating scan are shown in Fig.4(a)–(c),respectively.The detailed thermal characteristics,such as glass transition tempera-ture (T g ),crystallization temperatures (T c ),melting tem-perature (T m ),crystallization enthalpy during the
cooling
Fig.2.The in?uence of feed ratio of HDI and prepolymer on the chain-extending reaction.
28 F.Chen et al./European Polymer Journal 46(2010)24–33
F.Chen et al./European Polymer Journal46(2010)24–3329
Fig.3.(a)1H NMR spectra and(b)13C NMR spectra of LCB-PPDO.
scan(D H c1),the second crystallization enthalpy during the heating scan(D H c2)and the enthalpies of fusion(D H m)are all listed in Table3.
As shown in Fig.4(b),unlike linear PPDO,LCB-PPDOs have no crystallization observed during cooling.In the sub-sequent heating scan,it can be seen that the crystallization temperatures(T c)increase evidently with branch density. The LCB structure and the presence of heterogeneous seg-ments such as TMP,BD and amide in LCB-PPDO chains may disturb the crystallization of PPDO segments.
In order to further explain the phenomena,we intro-duce the conception of relative crystallinity(X c),which was calculated from the?rst and the second heating scan using the following equations:
X c?
D H m
D H0
?100%e4T
Table2
Molecular structure and rheological characteristics of LCB-PPDOs.
Sample M b(g/mol)M r B n g0,120°C(Pa s)n a k(s)
LCB-208100 1.25 6.95020.32 5.9
LCB-4014,0000.96 3.84220.43 2.3
LCB-6023,800 1.32 2.03990.390.85
PPDO––01970.990.15
a Shear-thinning
index.
Fig.4.DSC patterns of LCB-PPDO and linear PPDO:(a)the?rst heating scan;(b)cooling scan;(c)the second heating scan.
Table3
Thermal characteristics of LCBPPDO and Linear PPDO from DSC patterns.
Sample The?rst heating scan The cooling scan The second heating scan
T g(°C)T m(°C)D H m(J/g)X c(%)T g(°C)T c(°C)D H c1(J/g)T g(°C)T c(°C)D H c2(J/g)T m(°C)D H m(J/g)X c(%)
LCB-20à19.790.555.839.6à20.7––à18.559.011.789.913.49.5 LCB-40à23.596.560.342.8à23.9––à20.844.549.297.352.937.5 LCB-60à18.9100.769.249.1à18.335.80.8à16.242.450.3101.161.943.9 PPDOà15.0104.673.051.8à16.439.319.2à14.234.934.4104.371.550.7 30 F.Chen et al./European Polymer Journal46(2010)24–33
where D H m is the speci?c enthalpy of melting for the ?rst and the second heating scan and D H 0is the melt enthalpy of the hypothetically 100%crystalline PPDO (D H 0=141J/g)[20].The detailed data were listed in Table 3.It is docu-mented that a high degree of branching in a polymer back-bone provides lower crystallinity,for the case of symmetric chains that easily crystallize,than a linear polymer with equal molecular weight [21].The X c1of LCB-PPDOs from the ?rst heating scan is lower than that of linear PPDO,and is decreased with the increase of branch density,indicating that the presence of branching structure and heterogeneous segments may frustrate the crystallization process of PPDO segments and therefore decrease the de-gree of crystallinity even after the consummate crystalliza-tion process.Moreover,during the second heating scan,the crystallinity of LCB-PPDOs was lower than that during the ?rst heating scan,and the difference between two heating scans decreased with the increase of branch density.The introduction of heterogenous molecular segments from initiator and chain extender may also decrease the crystal-lization rate of PPDO segments and the samples could not crystallize completely during the cooling and following second heating scan with 10°C of heating and cooling rate [15].The LCB-PPDO with higher branch density has higher content of heterogeneous molecular segments from BD,TMP,and HDI,and therefore resulted in a much smaller degree of crystallinity than those of linear PPDO and LCB-PPDO with lower branch density during the second heating scan.
The XRD patterns of linear PPDO and LCB-PPDOs are shown in Fig.5.Obvious re?ections are observed at 2h =22°,24°and 29°,assigned to 210,020and 310planes,respectively [22],It is clear that the XRD pro?les of LCB-PPDOs are almost identical as those of linear PPDO,indicated that the crystallization was decided by PPDO seg-ments,and the introduction of LCB structure and heteroge-neous segments did not disturb the unit-cell dimensions of PPDO segments.This result is in good accordance with those of star-branched PPDO [13]and linear chain-extended PPDO using isocyanate as extender [15]reported before.
3.5.Rheological properties of LCB-PPDOs
The Small-Amplitude Dynamic Oscillatory Shear mea-surement was used to study the rheological properties of LCB-PPDOs.The shear rheological behavior of macromole-cules is very sensitive to the topological structure.The presence of very small amounts of LCB can in?uence the zero-shear viscosity (g 0),the complex viscosity (g *)and the degree of shear thinning,as compared to the linear polymers with similar molecular weight [23–25].Fig.6showed the complex viscosities of the LCB-PPDOs and Lin-ear PPDO.From this ?gure,it was readily apparent that the branch density had a signi?cant in?uence on the complex viscosity over the entire frequency range studied.The shear thinning of LCB-PPDOs started at lower frequency than that of linear PPDO.Unlike linear PPDO,no obvious Newonian-plateau was observed for LCB-PPDOs at low fre-quency which can be attributed to the long relaxation times of branched polymers.The branches of LCB-PPDOs may form suf?cient entanglements with each other and the number of entanglements increased with branch den-sity.Therefore,LCB-PPDOs exhibit a higher complex vis-cosity than linear PPDO with similar molecular weight,and the complex viscosities of LCB-PPDOs increased with the branch density at low frequency.While at high fre-quency,the LCB-PPDOs exhibited a lower viscosity than linear PPDO owning to a higher degree of shear thinning.Furthermore,the extent of shear thinning was increased with branch density of the LCB-PPDOs.The viscosity of the samples could be ?tted by the Cross equation [26],given by Eq.(5):
g ?ex T?
g 0
1tek x Tn
e5T
where k is relaxation time,g 0is zero-shear viscosity,and n is shear-thinning index,which indicates the degree of non-Newonian behavior.These values are all listed in Table 2.LCB-PPDOs exhibit much higher zero-shear viscosity,higher relaxation time and lower shear-thinning index comparing to those of linear PPDO.In addition,the g 0of the LCB-PPDOs and relaxation time increased while the shear-thinning
in-
Fig.5.XRD curves of the PPDO and
LCB-PPDOs.
https://www.wendangku.net/doc/7e8568447.html,plex viscosities versus angle frequency of the LCB-PPDOs and PPDO at 120°C.
F.Chen et al./European Polymer Journal 46(2010)24–3331
dex decreased with the increase of the branch density.Since those LCB-PPDOs used for rheological characterization have similar molecular weight,the changes in LCB structure should be the main reason for such results.Similar phenom-ena were also observed for other LCB polymers [25,27–30].Besides zero-shear viscosity,other properties such as the storage and loss moduli (G 0,G 00)were also in?uenced by LCB [24,30–32].Fig.7showed the storage modulus G’plotted as a function of angular frequencies at a reference temperature of 120°C for LCB-PPDOs and linear PPDO.The G’of linear PPDO increased with frequency and the slope of G 0approached 2at low frequency.Whereas LCB-PPDOs were observed to have broadened G 0with slopes only approached 1.3at low frequencies measured,and de-creased with the increase of branch density,indicating the relaxation times increased with the increase of the branch density of the polymers.LCB added a mode of relaxation at low frequency,which was not present in the linear PPDO.The master curves of storage and loss modulus of LCB-20and linear PPDO were shown in Fig.8with the remainders omitted to prevent crowding.At lower frequencies,linear PPDO followed the well-known frequency dependence,which was usually observed for linear polymers,i.e.,G 0and G 00became proportional to x 2and x ,respectively.It was apparent that LCB-20had signi?cantly higher values of G 0and G 00than linear PPDO at low frequencies,while at the high frequencies x c ,a crossover between G 0and G 00curves of LCB-20was observed.Moreover,no propor-tionality of G 0and G 00to x 2and x was observed for LCB-PPDOs at the lowest frequencies measured,which con-?rmed the presence of long-chain-branched structure.The relaxation time determined from s =1/x c ,where x c is the frequency at which the G 0and G 00curves cross each other,is in good accordance with that of calculated from Eq.(5).
The frequency independency of loss tangent tan (d ) G 00/G 0has been widely used for examining LCB poly-mers [24,25,33].Fig.9indicates tan d as a function of fre-quencies for LCB-PPDOs and linear PPDO.For PPDO,tan d increased intensively with the increase of frequency,which was a typical terminal behavior of liquid-like material.For LCB-PPDOs,tan d was lower than that of linear PPDO at the
same frequency;moreover,it decreased with the increase of branch density of LCB-PPDOs.As mentioned previously,the relaxation time was determined by x c ,a frequency at which the G 0and G 00curves cross each other,and tan (d )is equal to 1at the crossover.Because tan d decreased with the increase of branch density of LCB-PPDOs at the same frequency,x c decreased with the increase of branch den-sity,indicating the relaxation take place at a lower fre-quency for high branch density LCB-PPDO.4.Conclusions
PPDO’s with long-chain branches (LCB-PPDOs)have been successfully synthesized via the reaction between the terminated hydroxyl groups of linear bi-functional and star-shape tri-functional PPDO prepolymers using HDI as the chain-extending agent.The average number of branch per 100,000g/mol (B n )and branch length of LCB-PPDOs can be controlled by changing the chain length of prepolymers,and range from 0to 6.72branch points per 100,000g/mol and from 6900g/mol to 20,500g/mol,respectively,according to the results calculated from 1H NMR.The undesired gelation reaction could be
also
Fig.7.Storage modulus of the LCB-PPDOs and PPDO at 120°
C.
Fig.8.Master curves of storage and loss modulus of LCB-20and PPDO at 120°
C.
Fig.9.Tan d versus angle frequent for the LCB-PPDOs and PPDO at 120°C.
32 F.Chen et al./European Polymer Journal 46(2010)24–33
depressed successfully by adjusting the chain length and content of tri-functional prepolymers.The crystalline tem-perature T c of LCB-PPDOs increases,and the relative crys-tallinity X c and crystallization rates decrease evidently with the increase of branch density,but the crystalline structure has not been disturbed according to the results investigated by DSC and XRD technique.Small-amplitude oscillatory shear experiments show that the LCB structures have obvious in?uence on the rheological properties of PPDO.As the branch density of PPDO increases,zero-shear viscosity g0,G0at low frequency and relaxation times k increase,whilst the shear-thinning index n and loss angle decrease,which are in accordance with those of represen-tative LCB polymers.Therefore,the rheological behaviors of PPDO can be well-controlled via synthesizing LCB-PPDOs with the desired architectures.
Acknowledgement
This work was supported?nancially by the National Natural Science Foundation of China(No.20874065, 50525309),the Research Fund for the Doctoral Program of Ministry of Education of China(No.200806100012) and the National Key Technology R&D Program(2007BAE 28B06).The Analytical and Testing Center of Sichuan Uni-versity provided NMR analysis.
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从实践的角度探讨在日语教学中多媒体课件的应用
从实践的角度探讨在日语教学中多媒体课件的应用 在今天中国的许多大学，为适应现代化，信息化的要求，建立了设备完善的适应多媒体教学的教室。许多学科的研究者及现场教员也积极致力于多媒体软件的开发和利用。在大学日语专业的教学工作中，教科书、磁带、粉笔为主流的传统教学方式差不多悄然向先进的教学手段而进展。 一、多媒体课件和精品课程的进展现状 然而，目前在专业日语教学中能够利用的教学软件并不多见。比如在中国大学日语的专业、第二外語用教科书常见的有《新编日语》（上海外语教育出版社）、《中日交流标准日本語》（初级、中级）（人民教育出版社）、《新编基础日语（初級、高級）》（上海译文出版社）、《大学日本语》（四川大学出版社）、《初级日语》《中级日语》（北京大学出版社）、《新世纪大学日语》（外语教学与研究出版社）、《综合日语》（北京大学出版社）、《新编日语教程》（华东理工大学出版社）《新编初级（中级）日本语》（吉林教育出版社）、《新大学日本语》（大连理工大学出版社）、《新大学日语》（高等教育出版社）、《现代日本语》（上海外语教育出版社）、《基础日语》（复旦大学出版社）等等。配套教材以录音磁带、教学参考、习题集为主。只有《中日交流標準日本語（初級上）》、《初級日语》、《新编日语教程》等少数教科书配备了多媒体DVD视听教材。 然而这些试听教材，有的内容为日语普及读物，并不适合专业外语课堂教学。比如《新版中日交流标准日本语（初级上）》，有的尽管DVD视听教材中有丰富的动画画面和语音练习。然而，课堂操作则花费时刻长，不利于教师重点指导，更加适合学生的课余练习。比如北京大学的《初级日语》等。在这种情形下，许多大学的日语专业致力于教材的自主开发。 其中，有些大学的还推出精品课程，取得了专门大成绩。比如天津外国语学院的《新编日语》多媒体精品课程为2007年被评为“国家级精品课”。目前已被南开大学外国语学院、成都理工大学日语系等全国40余所大学推广使用。
常用介词的用法
分考点1 表示时间的介词 Point 1 at, in, on 的用法 （1）at 的用法 At 表示时间点，用于具体的时刻（几点，正午，午夜，黎明，拂晓，日出，日落等），或把某一时间看作某一时刻的词之前以及某些节假日的词之前。 at 6：00 在6点钟 At noon 在中午 At daybreak 在拂晓 At down 在黎明 At Christmas 在圣诞节 【特别注意】在以下的时间短语中，at 表示时间段。 At dinner time 在（吃）晚饭时 At weekends/ the weekend 在周末 （2）in 的用法 ①表示时间段，与表示较长一段时间的词搭配，如年份，月份，季节，世纪，朝代，还可以用于泛指的上午、下午、傍晚等时间段的词前。 In 2009 在2009年 In April 在四月 In the 1990s 在20世纪90年代 In Tang Dynasty 在唐朝 In the morning在上午 ②后接时间段，用于将来时，表示“在一段时间之后”。 The film will begin in an hour. 电影将于一个小时之后开始。 【特别注意】当时间名词前有this，that，last，next，every，each，some等词修饰时，通常不用任何介词。 This morning 今天上午last year 去年 （3）on 的用法 ①表示在特定的日子、具体的日期、星期几、具体的某一天或某些日子。 On September the first 在9月1号 On National Day 在国庆节 We left the dock on a beautiful afternoon. 我们在一个明媚的下午离开了码头。 ②表示在具体的某一天的上午、下午或晚上（常有前置定语或后置定语修饰）。 On Sunday morning 在星期日的早上 On the night of October 1 在10月1号的晚上 【特别注意】“on +名词或动名词”表示“一...就...”. On my arrival home/ arriving home, I discovered they had gone. 我一到家就发现他们已经离开了。 Point 2 in，after 的用法 In 和after都可以接时间段，表示“在...之后”，但in 常与将来时连用，after 常与过去时连用。 We will meet again in two weeks.
英语介词用法大全
英语介词用法大全 TTA standardization office【TTA 5AB- TTAK 08- TTA 2C】
介词（The Preposition）又叫做前置词，通常置于名词之前。它是一种虚词，不需要重读，在句中不单独作任何句子成分，只表示其后的名词或相当于名词的词语与其他句子成分的关系。中国学生在使用英语进行书面或口头表达时，往往会出现遗漏介词或误用介词的错误，因此各类考试语法的结构部分均有这方面的测试内容。 1. 介词的种类 英语中最常用的介词，按照不同的分类标准可分为以下几类： (1). 简单介词、复合介词和短语介词 ①.简单介词是指单一介词。如： at , in ,of ,by , about , for, from , except , since, near, with 等。②. 复合介词是指由两个简单介词组成的介词。如： Inside, outside , onto, into , throughout, without , as to as for , unpon, except for 等。 ③. 短语介词是指由短语构成的介词。如： In front of , by means o f, on behalf of, in spite of , by way of , in favor of , in regard to 等。 (2). 按词义分类 {1} 表地点（包括动向）的介词。如： About ,above, across, after, along , among, around , at, before, behind, below, beneath, beside, between , beyond ,by, down, from, in, into , near, off, on, over, through, throught, to, towards,, under, up, unpon, with, within , without 等。 {2} 表时间的介词。如： About, after, around , as , at, before , behind , between , by, during, for, from, in, into, of, on, over, past, since, through, throughout, till(until) , to, towards , within 等。 {3} 表除去的介词。如： beside , but, except等。 {4} 表比较的介词。如： As, like, above, over等。 {5} 表反对的介词。如： againt ,with 等。 {6} 表原因、目的的介词。如： for, with, from 等。 {7} 表结果的介词。如： to, with , without 等。 {8} 表手段、方式的介词。如： by, in ,with 等。 {9} 表所属的介词。如： of , with 等。 {10} 表条件的介词。如：
新视野大学英语全部课文原文
Unit1 Americans believe no one stands still. If you are not moving ahead, you are falling behind. This attitude results in a nation of people committed to researching, experimenting and exploring. Time is one of the two elements that Americans save carefully, the other being labor. "We are slaves to nothing but the clock,” it has been said. Time is treated as if it were something almost real. We budget it, save it, waste it, steal it, kill it, cut it, account for it; we also charge for it. It is a precious resource. Many people have a rather acute sense of the shortness of each lifetime. Once the sands have run out of a person’s hourglass, they cannot be replaced. We want every minute to count. A foreigner’s first impression of the U.S. is li kely to be that everyone is in a rush -- often under pressure. City people always appear to be hurrying to get where they are going, restlessly seeking attention in a store, or elbowing others as they try to complete their shopping. Racing through daytime meals is part of the pace
英语介词用法详解
英语常用介词用法与辨析 ■表示方位的介词：in, to, on 1. in 表示在某地范围之内。如： Shanghai is/lies in the east of China. 上海在中国的东部。 2. to 表示在某地范围之外。如： Japan is/lies to the east of China. 日本位于中国的东面。 3. on 表示与某地相邻或接壤。如： Mongolia is/lies on the north of China. 蒙古国位于中国北边。 ■表示计量的介词：at, for, by 1. at表示“以……速度”“以……价格”。如： It flies at about 900 kilometers a hour. 它以每小时900公里的速度飞行。 I sold my car at a high price. 我以高价出售了我的汽车。 2. for表示“用……交换，以……为代价”。如： He sold his car for 500 dollars. 他以五百元把车卖了。 注意：at表示单价(price) ，for表示总钱数。 3. by表示“以……计”，后跟度量单位。如： They paid him by the month. 他们按月给他计酬。 Here eggs are sold by weight. 在这里鸡蛋是按重量卖的。 ■表示材料的介词：of, from, in 1. of成品仍可看出原料。如： This box is made of paper. 这个盒子是纸做的。 2. from成品已看不出原料。如： Wine is made from grapes. 葡萄酒是葡萄酿成的。 3. in表示用某种材料或语言。如： Please fill in the form in pencil first. 请先用铅笔填写这个表格。 They talk in English. 他们用英语交谈(from 。 注意：in指用材料，不用冠词；而with指用工具，要用冠词。请比较：draw in penc il/draw with a pencil。 ■表示工具或手段的介词：by, with, on 1. by用某种方式，多用于交通。如by bus乘公共汽车，by e-mail. 通过电子邮件。
with的用法大全
with的用法大全----四级专项训练with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、 with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词; 2. with或without-名词/代词+副词; 3. with或without-名词/代词+介词短语; 4. with或without-名词/代词+动词不定式; 5. with或without-名词/代词+分词。 下面分别举例：
1、 She came into the room，with her nose red because of cold.(with+名词+形容词，作伴随状语) 2、 With the meal over ， we all went home.(with+名词+副词，作时间状语) 3、The master was walking up and down with the ruler under his arm。(with+名词+介词短语，作伴随状语。) The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.(with+名词+不定式，作伴随状语) He could not finish it without me to help him.(without+代词 +不定式，作条件状语) 5、She fell asleep with the light burning.(with+名词+现在分词，作伴随状语) 6、Without anything left in the cupboard， she went out to get something to eat.(without+代词+过去分词，作为原因状语) 二、with结构的用法 在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件(详见上述例句)。
新视野大学英语第三版第二册课文语法讲解 Unit4
新视野三版读写B2U4Text A College sweethearts 1I smile at my two lovely daughters and they seem so much more mature than we,their parents,when we were college sweethearts.Linda,who's21,had a boyfriend in her freshman year she thought she would marry,but they're not together anymore.Melissa,who's19,hasn't had a steady boyfriend yet.My daughters wonder when they will meet"The One",their great love.They think their father and I had a classic fairy-tale romance heading for marriage from the outset.Perhaps,they're right but it didn't seem so at the time.In a way, love just happens when you least expect it.Who would have thought that Butch and I would end up getting married to each other?He became my boyfriend because of my shallow agenda:I wanted a cute boyfriend! 2We met through my college roommate at the university cafeteria.That fateful night,I was merely curious,but for him I think it was love at first sight."You have beautiful eyes",he said as he gazed at my face.He kept staring at me all night long.I really wasn't that interested for two reasons.First,he looked like he was a really wild boy,maybe even dangerous.Second,although he was very cute,he seemed a little weird. 3Riding on his bicycle,he'd ride past my dorm as if"by accident"and pretend to be surprised to see me.I liked the attention but was cautious about his wild,dynamic personality.He had a charming way with words which would charm any girl.Fear came over me when I started to fall in love.His exciting"bad boy image"was just too tempting to resist.What was it that attracted me?I always had an excellent reputation.My concentration was solely on my studies to get superior grades.But for what?College is supposed to be a time of great learning and also some fun.I had nearly achieved a great education,and graduation was just one semester away.But I hadn't had any fun;my life was stale with no component of fun!I needed a boyfriend.Not just any boyfriend.He had to be cute.My goal that semester became: Be ambitious and grab the cutest boyfriend I can find. 4I worried what he'd think of me.True,we lived in a time when a dramatic shift in sexual attitudes was taking place,but I was a traditional girl who wasn't ready for the new ways that seemed common on campus.Butch looked superb!I was not immune to his personality,but I was scared.The night when he announced to the world that I was his girlfriend,I went along
高中英语45个介词的基本用法
——45个基本介词的用法 1、about 【原始含义】 a-b-out “A在B外面” 【引申含义】 [prep] （1）在…到处，在…各处here and there eg: We wandered about the town for an hour or so. He looked about the room. （2）在…附近next to a place eg. She lives about the office. （3）关于in connection with eg: a book about English study I don’t know what you are talking about. [adv] （1）大约close to eg: We left there about 10 o’clock. It costs about 500 dollars. （2）到处，各处 eg: The children were rushing about in the garden. （3）在附近 eg : There is no food about. 【常见搭配】 作介词时的搭配: 一.动词+(about+名词) （1）arrange (about sth) 安排关于某事（2）argue (about sth) 讨论某事 （3）ask (about sth) 询问关于某事（4）boast (about sb/sth) 吹嘘... （5）care (about sb/sth)关心…,对…感兴趣（6）chat(about sth) 谈论某事（7）complain(about sb/sth) 抱怨… （8）dream (about sb/sth) 梦见某人/某物（9）go (about sth) 着手做...；从事...
with用法归纳
with用法归纳 （1）“用……”表示使用工具，手段等。例如： ①We can walk with our legs and feet. 我们用腿脚行走。 ②He writes with a pencil. 他用铅笔写。 （2）“和……在一起”，表示伴随。例如： ①Can you go to a movie with me? 你能和我一起去看电影'>电影吗？ ②He often goes to the library with Jenny. 他常和詹妮一起去图书馆。 （3）“与……”。例如： I’d like to have a talk with you. 我很想和你说句话。 （4）“关于，对于”，表示一种关系或适应范围。例如： What’s wrong with your watch? 你的手表怎么了？ （5）“带有，具有”。例如： ①He’s a tall kid with short hair. 他是个长着一头短发的高个子小孩。 ②They have no money with them. 他们没带钱。 （6）“在……方面”。例如： Kate helps me with my English. 凯特帮我学英语。 （7）“随着，与……同时”。例如： With these words, he left the room. 说完这些话，他离开了房间。 [解题过程] with结构也称为with复合结构。是由with+复合宾语组成。常在句中做状语，表示谓语动作发生的伴随情况、时间、原因、方式等。其构成有下列几种情形： 1.with+名词(或代词)+现在分词 此时，现在分词和前面的名词或代词是逻辑上的主谓关系。 例如:1)With prices going up so fast, we can't afford luxuries. 由于物价上涨很快，我们买不起高档商品。（原因状语） 2)With the crowds cheering, they drove to the palace. 在人群的欢呼声中，他们驱车来到皇宫。（伴随情况） 2.with+名词(或代词)+过去分词 此时，过去分词和前面的名词或代词是逻辑上的动宾关系。
新视野大学英语读写教程第一册课文翻译及课后答案
Unit 1 1学习外语是我一生中最艰苦也是最有意义的经历之一。虽然时常遭遇挫折，但却非常有价值。 2我学外语的经历始于初中的第一堂英语课。老师很慈祥耐心，时常表扬学生。由于这种积极的教学方法，我踊跃回答各种问题，从不怕答错。两年中，我的成绩一直名列前茅。 3到了高中后，我渴望继续学习英语。然而，高中时的经历与以前大不相同。以前，老师对所有的学生都很耐心，而新老师则总是惩罚答错的学生。每当有谁回答错了，她就会用长教鞭指着我们，上下挥舞大喊：“错！错！错！”没有多久，我便不再渴望回答问题了。我不仅失去了回答问题的乐趣，而且根本就不想再用英语说半个字。 4好在这种情况没持续多久。到了大学，我了解到所有学生必须上英语课。与高中老师不。大学英语老师非常耐心和蔼，而且从来不带教鞭！不过情况却远不尽如人意。由于班大，每堂课能轮到我回答的问题寥寥无几。上了几周课后，我还发现许多同学的英语说得比我要好得多。我开始产生一种畏惧感。虽然原因与高中时不同，但我却又一次不敢开口了。看来我的英语水平要永远停步不前了。 5直到几年后我有机会参加远程英语课程，情况才有所改善。这种课程的媒介是一台电脑、一条电话线和一个调制解调器。我很快配齐了必要的设备并跟一个朋友学会了电脑操作技术，于是我每周用5到7天在网上的虚拟课堂里学习英语。 6网上学习并不比普通的课堂学习容易。它需要花许多的时间，需要学习者专心自律，以跟上课程进度。我尽力达到课程的最低要求，并按时完成作业。 7我随时随地都在学习。不管去哪里，我都随身携带一本袖珍字典和笔记本，笔记本上记着我遇到的生词。我学习中出过许多错，有时是令人尴尬的错误。有时我会因挫折而哭泣，有时甚至想放弃。但我从未因别的同学英语说得比我快而感到畏惧，因为在电脑屏幕上作出回答之前，我可以根据自己的需要花时间去琢磨自己的想法。突然有一天我发现自己什么都懂了，更重要的是，我说起英语来灵活自如。尽管我还是常常出错，还有很多东西要学，但我已尝到了刻苦学习的甜头。 8学习外语对我来说是非常艰辛的经历，但它又无比珍贵。它不仅使我懂得了艰苦努力的意义，而且让我了解了不同的文化，让我以一种全新的思维去看待事物。学习一门外语最令人兴奋的收获是我能与更多的人交流。与人交谈是我最喜欢的一项活动，新的语言使我能与陌生人交往，参与他们的谈话，并建立新的难以忘怀的友谊。由于我已能说英语，别人讲英语时我不再茫然不解了。我能够参与其中，并结交朋友。我能与人交流，并能够弥合我所说的语言和所处的文化与他们的语言和文化之间的鸿沟。 III. 1. rewarding 2. communicate 3. access 4. embarrassing 5. positive 6. commitment 7. virtual 8. benefits 9. minimum 10. opportunities IV. 1. up 2. into 3. from 4. with 5. to 6. up 7. of 8. in 9. for 10.with V. 1.G 2.B 3.E 4.I 5.H 6.K 7.M 8.O 9.F 10.C Sentence Structure VI. 1. Universities in the east are better equipped, while those in the west are relatively poor. 2. Allan Clark kept talking the price up, while Wilkinson kept knocking it down. 3. The husband spent all his money drinking, while his wife saved all hers for the family. 4. Some guests spoke pleasantly and behaved politely, while others wee insulting and impolite. 5. Outwardly Sara was friendly towards all those concerned, while inwardly she was angry. VII. 1. Not only did Mr. Smith learn the Chinese language, but he also bridged the gap between his culture and ours. 2. Not only did we learn the technology through the online course, but we also learned to communicate with friends in English. 3. Not only did we lose all our money, but we also came close to losing our lives.
新大学日语简明教程课文翻译
新大学日语简明教程课文翻译 第21课 一、我的留学生活 我从去年12月开始学习日语。已经3个月了。每天大约学30个新单词。每天学15个左右的新汉字，但总记不住。假名已经基本记住了。 简单的会话还可以，但较难的还说不了。还不能用日语发表自己的意见。既不能很好地回答老师的提问，也看不懂日语的文章。短小、简单的信写得了，但长的信写不了。 来日本不久就迎来了新年。新年时，日本的少女们穿着美丽的和服，看上去就像新娘。非常冷的时候，还是有女孩子穿着裙子和袜子走在大街上。 我在日本的第一个新年过得很愉快，因此很开心。 现在学习忙，没什么时间玩，但周末常常运动，或骑车去公园玩。有时也邀朋友一起去。虽然我有国际驾照，但没钱，买不起车。没办法，需要的时候就向朋友借车。有几个朋友愿意借车给我。 二、一个房间变成三个 从前一直认为睡在褥子上的是日本人，美国人都睡床铺，可是听说近来纽约等大都市的年轻人不睡床铺，而是睡在褥子上，是不是突然讨厌起床铺了？ 日本人自古以来就睡在褥子上，那自有它的原因。人们都说日本人的房子小，从前，很少有人在自己的房间，一家人住在一个小房间里是常有的是，今天仍然有人过着这样的生活。 在仅有的一个房间哩，如果要摆下全家人的床铺，就不能在那里吃饭了。这一点，褥子很方便。早晨，不需要褥子的时候，可以收起来。在没有了褥子的房间放上桌子，当作饭厅吃早饭。来客人的话，就在那里喝茶；孩子放学回到家里，那房间就成了书房。而后，傍晚又成为饭厅。然后收起桌子，铺上褥子，又成为了全家人睡觉的地方。 如果是床铺的话，除了睡觉的房间，还需要吃饭的房间和书房等，但如果使用褥子，一个房间就可以有各种用途。 据说从前，在纽约等大都市的大学学习的学生也租得起很大的房间。但现在房租太贵，租不起了。只能住更便宜、更小的房间。因此，似乎开始使用睡觉时作床，白天折小能成为椅子的、方便的褥子。
介词with的用法大全
介词with的用法大全 With是个介词，基本的意思是“用”，但它也可以协助构成一个极为多采多姿的句型，在句子中起两种作用；副词与形容词。 with在下列结构中起副词作用： 1.“with+宾语+现在分词或短语”，如： (1) This article deals with common social ills, with particular attention being paid to vandalism. 2.“with+宾语+过去分词或短语”，如： (2) With different techniques used, different results can be obtained. (3) The TV mechanic entered the factory with tools carried in both hands. 3.“with+宾语+形容词或短语”，如： (4) With so much water vapour present in the room, some iron-made utensils have become rusty easily. (5) Every night, Helen sleeps with all the windows open. 4.“with+宾语＋介词短语”，如： (6) With the school badge on his shirt, he looks all the more serious. (7) With the security guard near the gate no bad character could do any thing illegal. 5.“with+宾语＋副词虚词”，如： (8) You cannot leave the machine there with electric power on. (9) How can you lock the door with your guests in? 上面五种“with”结构的副词功能，相当普遍，尤其是在科技英语中。 接着谈“with”结构的形容词功能，有下列五种： 一、“with+宾语+现在分词或短语”，如： (10) The body with a constant force acting on it. moves at constant pace. (11) Can you see the huge box with a long handle attaching to it ? 二、“with+宾语+过去分词或短语” (12) Throw away the container with its cover sealed. (13) Atoms with the outer layer filled with electrons do not form compounds. 三、“with+宾语+形容词或短语”，如： (14) Put the documents in the filing container with all the drawers open.
新视野大学英语第一册Unit 1课文翻译
新视野大学英语第一册Unit 1课文翻译 学习外语是我一生中最艰苦也是最有意义的经历之一。 虽然时常遭遇挫折，但却非常有价值。 我学外语的经历始于初中的第一堂英语课。 老师很慈祥耐心，时常表扬学生。 由于这种积极的教学方法，我踊跃回答各种问题，从不怕答错。 两年中，我的成绩一直名列前茅。 到了高中后，我渴望继续学习英语。然而，高中时的经历与以前大不相同。 以前，老师对所有的学生都很耐心，而新老师则总是惩罚答错的学生。 每当有谁回答错了，她就会用长教鞭指着我们，上下挥舞大喊：“错！错！错！” 没有多久，我便不再渴望回答问题了。 我不仅失去了回答问题的乐趣，而且根本就不想再用英语说半个字。 好在这种情况没持续多久。 到了大学，我了解到所有学生必须上英语课。 与高中老师不同，大学英语老师非常耐心和蔼，而且从来不带教鞭！ 不过情况却远不尽如人意。 由于班大，每堂课能轮到我回答的问题寥寥无几。 上了几周课后，我还发现许多同学的英语说得比我要好得多。 我开始产生一种畏惧感。 虽然原因与高中时不同，但我却又一次不敢开口了。 看来我的英语水平要永远停步不前了。 直到几年后我有机会参加远程英语课程，情况才有所改善。 这种课程的媒介是一台电脑、一条电话线和一个调制解调器。 我很快配齐了必要的设备并跟一个朋友学会了电脑操作技术，于是我每周用5到7天在网上的虚拟课堂里学习英语。 网上学习并不比普通的课堂学习容易。 它需要花许多的时间，需要学习者专心自律，以跟上课程进度。 我尽力达到课程的最低要求，并按时完成作业。 我随时随地都在学习。 不管去哪里，我都随身携带一本袖珍字典和笔记本，笔记本上记着我遇到的生词。 我学习中出过许多错，有时是令人尴尬的错误。 有时我会因挫折而哭泣，有时甚至想放弃。 但我从未因别的同学英语说得比我快而感到畏惧，因为在电脑屏幕上作出回答之前，我可以根据自己的需要花时间去琢磨自己的想法。 突然有一天我发现自己什么都懂了，更重要的是，我说起英语来灵活自如。 尽管我还是常常出错，还有很多东西要学，但我已尝到了刻苦学习的甜头。 学习外语对我来说是非常艰辛的经历，但它又无比珍贵。 它不仅使我懂得了艰苦努力的意义，而且让我了解了不同的文化，让我以一种全新的思维去看待事物。 学习一门外语最令人兴奋的收获是我能与更多的人交流。 与人交谈是我最喜欢的一项活动，新的语言使我能与陌生人交往，参与他们的谈话，并建立新的难以忘怀的友谊。 由于我已能说英语，别人讲英语时我不再茫然不解了。 我能够参与其中，并结交朋友。
新大学日语阅读与写作1 第3课译文
习惯与礼仪 我是个漫画家，对旁人细微的动作、不起眼的举止等抱有好奇。所以，我在国外只要做错一点什么，立刻会比旁人更为敏锐地感觉到那个国家的人们对此作出的反应。 譬如我多次看到过，欧美人和中国人见到我们日本人吸溜吸溜地出声喝汤而面露厌恶之色。过去，日本人坐在塌塌米上，在一张低矮的食案上用餐，餐具离嘴较远。所以，养成了把碗端至嘴边吸食的习惯。喝羹匙里的东西也象吸似的，声声作响。这并非哪一方文化高或低，只是各国的习惯、礼仪不同而已。 日本人坐在椅子上围桌用餐是1960年之后的事情。当时，还没有礼仪规矩，甚至有人盘着腿吃饭。外国人看见此景大概会一脸厌恶吧。 韩国女性就座时，单腿翘起。我认为这种姿势很美，但习惯于双膝跪坐的日本女性大概不以为然，而韩国女性恐怕也不认为跪坐为好。 日本等多数亚洲国家，常有人习惯在路上蹲着。欧美人会联想起狗排便的姿势而一脸厌恶。 日本人常常把手放在小孩的头上说“好可爱啊！”，而大部分外国人会不愿意。 如果向回教国家的人们劝食猪肉和酒，或用左手握手、递东西，会不受欢迎的。当然，饭菜也用右手抓着吃。只有从公用大盘往自己的小盘里分食用的公勺是用左手拿。一旦搞错，用黏糊糊的右手去拿，
会遭人厌恶。 在欧美，对不受欢迎的客人不说“请脱下外套”，所以电视剧中的侦探哥隆波总是穿着外套。访问日本家庭时，要在门厅外脱掉外套后进屋。穿到屋里会不受欢迎的。 这些习惯只要了解就不会出问题，如果因为不知道而遭厌恶、憎恨，实在心里难受。 过去，我曾用色彩图画和简短的文字画了一本《关键时刻的礼仪》（新潮文库）。如今越发希望用各国语言翻译这本书。以便能对在日本的外国人有所帮助。同时希望有朝一日以漫画的形式画一本“世界各国的习惯与礼仪”。 练习答案 ５、 （１）止める並んでいる見ているなる着色した （２）拾った入っていた行ったしまった始まっていた
介词at的基本用法
介词at的基本用法： 一、at引导的时间短语通常可表示： 1.在几点几分，例如：at one o’clock(在一点钟) I usually make the bed at one o’clock.. 2.在用餐时间，例如：at lunchtime（在午餐时间） 3.在某个节日，例如：at Christmas 在圣诞节的时候 4.在某个年龄的时候，例如：at the age of 12。在12岁的时候 5.一天中的某段较短的时间，例如：at noon在中午at night在夜里 二、at也可引导地点短语，常用于小地点之前，例如： at the bus stop在汽车站at the butcher’s 在肉店里at school在学校里at home在家里 介词on的基本用法： 一、on可引导地点短语，表示“在…上面”，例如：on the table在桌子上 二、on也可引导时间短语，通常有以下用法： 1.用于“星期”和“月份”中的任何一天之前，例如：On Monday在星期一on April 1st. 2.用于某个“星期几”当天的某段时间，例如：on Monday morning在星期一上午 3.用于具体某一天之前，例如：on that day在那一天On my birthday在我的生日那天 On Christmas day在圣诞节那天 介词in的基本用法： 一、in可引导地点短语，常表示“在…里面”，例如：in the bag在袋子里 二、in引导的时间短于通常有以下用法： 1.在某个世纪，例如：in the 21st century在21世纪 2.在某一年，例如：in 1995在1995年 3.在某一个季节，例如：in spring在春季 4.在某一个月份，例如：in March在三月里 5.在某段时期，例如：in the holidays在假期里 6.在某个持续几天的节日里，例如：in Easter Week在复活周 7.在一天中的某段时间，例如：in the morning在上午（早晨）
初中 英语 介词“with”的用法
介词“with”的用法 1、同, 与, 和, 跟 talk with a friend 与朋友谈话 learn farming with an old peasant 跟老农学习种田 fight [quarrel, argue] with sb. 跟某人打架 [争吵, 辩论] [说明表示动作的词, 表示伴随]随着, 和...同时 change with the temperature 随着温度而变化 increase with years 逐年增加 be up with the dawn 黎明即起 W-these words he left the room. 他说完这些话便离开了房间。2 2、表示使用的工具, 手段 defend the motherland with one s life 用生命保卫祖国 dig with a pick 用镐挖掘 cut meat with a knife 用刀割肉3
3、说明名词, 表示事物的附属部分或所具有的性质]具有; 带有; 加上; 包括...在内 tea with sugar 加糖的茶水 a country with a long history 历史悠久的国家4 4、表示一致]在...一边, 与...一致; 拥护, 有利于 vote with sb. 投票赞成某人 with的复合结构作独立主格,表示伴随情况时，既可用分词的独立结构，也可用with的复合结构： with +名词(代词)+现在分词/过去分词/形容词/副词/不定式/介词短语。例如： He stood there, his hand raised. = He stood there, with his hand raise.他举手着站在那儿。 典型例题 The murderer was brought in, with his hands ___ behind his back A. being tied B. having tied C. to be tied D. tied 答案D. with +名词(代词)+分词+介词短语结构。当分词表示伴随状况时，其主语常常用