學生：陳雅貞指導教授：陳澄河教授日期 :99/12/22

INTRODUCTION

• PLA is produced either by the ring-opening polymerization of lactide or by the condensation polymerization of the lactic acid monomer.

• This weakness might be improved by blending or copolymerization of PLA with lower glass-transition temperature polymers, such as poly(e-caprolactone) (PCL).

• PCL is one of the typical aliphatic polyesters, and it is fully biodegradable, biocompatible, and nontoxic to living organisms.

• Preparing a PCL-b-PLA block copolymer can give a copolymer with the good properties of PLA and PCL, especially improving the brittle properties of PLA.

• The objective of this paper is the synthesis of PLA–PCL multiblock copolymer with a two-step reaction.

• Several analytical techniques ncluding acid value (AV) measurement, 1H-NMR analysis, gel permeation chromatography (GPC), and Fourier transform infrared spectroscopy (FTIR).

INTRODUCTION

Materials

• Lactic acid (LA)

• Tin (II) octoate

• chloroform (99%)

• poly(ε-caprolactone) diols(PCLD)

• HDI

Synthesis of PLA–PCL prepolymer

L-Lactic acid

Tin (II) octoate

condensation polymerized

170 ℃ reduced pressure of 20 mbar 100 rmp 20 hr

PCL-diols

PLA prepolymer

PLA prepolymer

4 hrunder the same conditions

molten polymerization product

Chain extension

Prepolymer (60 g)

0.3 g of catalyst

purged with a continuous flow of nitrogen

180 , 40min℃

1,6 -hexamethylene diisocyanate (HDI)

polymer

Results and discussion

AVs, defined as the weight in milligrams of KOH required to neutralize 1 g of the polymer.

AV is too high excess amount of carboxyl group after condensation reaction hinder the chain extension reaction AV should be as low as possible

The acid number decreases with increase in the PCL-diol ratio acid-containing groups such as lactic acid monomer and lactic acid oligomer have reacted almost completely with the hydroxyl-terminated chains.

Results and discussion

Mn decreased with increase in PCL content.Polycondensation is a reversible reaction Lactic acid

carboxylic acid group and hydroxyl group PCL-diol is added hydroxyl group is more than that of the carboxyl hydrolysis

Results and discussionPCL-diols

-CH2

adjacent to the hydroxy end group

3.65 ppm

3.65 ppm disappearance LA is reactive with PCL-diols

PLA-b-PCL copolymer1.6 ppm

5.1 ppm

(CH, PLA)

(CH3, PLA)

Results and discussion

The peaks at 3.5 and 4.3 are assigned to the proton adjacent to the hydroxyl end group of the PLA–PCL prepolymer.The peaks at 3.5 and 4.3 are assigned to the proton adjacent to the hydroxyl end group of the PLA–PCL prepolymer.

Figure 2. 1H-NMR spectrum of PLA–PCL prepolymer.

Results and discussion

Figure 3. TG analysis for the PLA–PCL prepolymer (PCL content: 10 wt%).

5wt% of the prepolymer is lost around 180℃

Many researchers have reported that the Polymer blends of PLA and PCL are immiscible DSC of the blends of PLA and PCL exhibit two melting peak

PLA-PCL copolymers Only one endothermic peak not polymer blends but copolymers

Results and discussion

–COO–

–COO–

–O–

–O–

Using diisocyanate as a chain extender

Figure 4. Infrared spectra of PLA–PCL prepolymer and chain extended product. (a) Sample of PLA–PCL prepolymer (PCL content: 10 wt%) and (b) sample of PLA–PCL chain extended products (NCO/OH=3).

1800–1400 cm-1 urethane bond formed by the reaction between –OH and –NCO groups is coincident with the carbonyl absorption (1760 cm-1).

Both spectra a and b exhibited characteristic ester absorption peaks (at 1750 and 1086 cm-1 for –COO– and –O–)Amide band of urethane bond also appears at 1525 cm-1 indicate that the reaction between –OH and –NCO groups took place.

Results and discussion

Figure 5. 1H-NMR spectrum of the PLA–PCL prepolymer and chain extended product. (A) The range of 2.0–5.0 ppm, (B) the range of 0–10ppm, (I) sample of PLA–PCL prepolymer (PCL content: 10wt%), and (II) sample of PLA–PCL chain extended products (NCO/OH=3). This figure is available in color online at www.interscience.wiley.com/journal/pat

4.36 ppm caused by the hydroxyl end group of the prepolymer disappeared as the reaction with diisocyanate proceeded.

The formation of urethane bond (CH2NHCOO) can be seen at 3.2 ppm

Indicated the reaction of HDI with the hydroxyl of the prepolymer took place.

Results and discussion

The molecular weights (both Mw and Mn) for samples PCLA1, PCLA2, and PCLA3 increased compared to PCLA0 because of chain extension.

When the NCO/OH ratio is over 3:1 the product formed a network Structure diisocyannate was used in excess, the isocyanate groups also react with the urethane groups and the result of this reaction is branched polymer chains

Results and discussion

Tg

b, c and d samples showed significantly higher Tg Chain extension by HDI increased the molecular weight and reduced the number of end groups, and thus reduced the free volumes.

Tg value decreased with an increase in the HDI content ratio unreacted HDI caused defects in the PLA–PCL matrix and disrupted the orderliness of the molecular arrangement.

Chain extended products were amorphous.

Figure 6. DSC thermo grams of the PLA–PCL prepolymer and chain extended products. This figure is available in color online at www.interscience. wiley.com/journal/pat

melting peak at 120 ℃

△ H=1.878 J/g

Tg

Results and discussion

As the NCO/OH ratio is raised, the tensile strength of the PLA–PCL chain extended products decreases, but the elongation at break of that is much improved.

The remarkable flexibility of the polymer is due to the PCL block present as the soft segment causes the great improvement of elongation at break

Conclusions

• The multiblock random copolymer of PLA–PCL with high molecular weight was successfully prepared through the melt polycondensation and the chain extension reaction.

• The weight average weight can reach 250,000 g/mol, when the PCL-diols content was 10 wt% and the NCO/OH ratio was 3:1.

• There was no melt peak on the DSC curve of the chain extended products; it indicated that the copolymers obtained were amorphous.