Preparation of Higher Molecular Weight Poly (L-lactic Acid) by Chain Extension

Table 1

The influences of process conditions on poly(lactic acid) after chain extension.

Run^a	𝑀𝜂pre (10^−4 g/mol)	[NCO]/[OH]^b	t (min)	[𝛼]𝐷^25	M (10^−4 g/mol)		𝑀𝑤/𝑀𝑛	Chain-extension efficiency (%)	Insoluble content (wt%)
					𝑀𝑛	𝑀𝑤
a1	2	1.5	20	−141	7.9	16.3	2.0	68.9	2.2
a2	2	3	20	−145	8.7	12.1	1.4	42.6	3.0
a3	2	6	20	−145	10.5	20.3	1.9	52.2	3.6
a4	2	8	20	−139	9.9	15.2	1.5	45.7	3.9
a5	2	6	10	−140	5.4	8.3	1.6	47.9	2.2
a6	2	6	30	−142	5.9	9.6	1.6	52.8	4.4
a7	2	6	40	−141	6.1	11.1	1.8	56.6	2.2
a8	3	6	20	−142	6.3	10.7	1.7	72.8	3.6
a9	4	6	20	−140	6.7	12.5	1.8	72.7	3.8
a10	5	6	20	−139	7.0	12.6	1.8	76.7	4.1

aReaction temperature: 175°C, nitrogen atmosphere; ^bmole ratio of –NCO to –OH.