Synthesis and characterization of new bi-sensitive copoly(2-oxazolines)

Figures & data

Table 1. Composition and characteristics of statistical copolymers from 2-cyclopropyl-2-oxazoline and 2-methoxycarbonylethyl-2-oxazoline.

Polymer	Cont. MEtOxa		Deg. of polym.		Molar mass Mn			Mn/Mw^b
	Theor. (mol%)	Exp.^a (mol%)	Theor.	Exp.^a	Theor. (g/mol)	NMR^a (g/mol)	SEC^b (g/mol)
st CP1	8.9	8.9	67	79	7765	9100	5100	1.96
st CP2	16.4	15.7	73	74	8708	8800	5900	1.86
st CP3	23.6	21.5	79	78	9681	9400	6200	1.77

Notes:

Molar feed of all polymerizations: 0.234 mmol 1,4-dibrombutene, 14.18 mmol 2-cyclopropyl-2-oxazoline, and indicated amount 2-methoxycarbonylethyl-2-oxazoline in 4.5 mL benzonitrile; reaction period 5 h.

^a Calculated from ¹H NMR signal integrals, estimated error is ±2 for degree of polymerization, and ±200 g/mol for M_n.

^b SEC results.

Table 2. Composition and characteristics of A-B-A block copolymers from 2-cyclopropyl-2-oxazoline (block B) and 2-methoxycarbonylethyl-2-oxazoline (block A).

Polymer	Units bl-B CPOxa		Units bl-A MEtOxa		Molar mass Mn			Mn/Mw^b
	Theor.	Exp.^a	Theor.	Exp.^a	Theor. (g/mol)	NMR^a (g/mol)	SEC^b (g/mol)
bl CP1	61	49	6.2	6	8772	7300	6200	1.8
bl CP2	61	56	12.5	12	10,750	10,000	7500	1.7
bl CP3	61	49	18	21	12,477	12,000	7200	2.1

Notes:

Molar feed of all polymerizations: 0.234 mmol 1,4-dibrombutene, 14.18 mmol 2-cyclopropyl-2-oxazoline (first stage), and indicated amount 2-methoxycarbonylethyl-2-oxazoline (second stage) in 4.5 mL benzonitrile.

^a Calculated from ¹H NMR signal integrals, estimated error is ±2 for monomer units, and ±200 g/mol for M_n.

^b SEC results.

Figure 1. ¹H (a,c) and ¹³C NMR spectra (b,d) of a statistical copolymer of CPOxa and MEtOxa (st CP2; a,b; solvent: CDCl₃) and the corresponding copolymer after hydrolysis (st CP2-H; c,d; solvent: D₂O).

Table 3. Phase transitions temperatures of CPOxa polymers and CPOxa/MEtOxa copolymers measured by turbidimetry.

Polymer	HP-1h	HP-4h	st CP1	st CP2	st CP3	bl CP1	bl CP2	bl CP3
Theor. ratio of MEtOxa/CPOxa	–	–	0.1	0.2	0.31	0.2	0.41	0.59
Exp.^a ratio of MEtOxa/CPOxa	–	–	0.1	0.19	0.27	0.24	0.43	0.86
Ttr (°C)	35.9	31.3	31.2	33.7	36.7	32.6	33.2	33.6

^a Calculated from ¹H NMR signal integrals.

Figure 2. Temperature-dependent turbidity measurements of statistical copolymers from CPOxa and MEtOxa.

Figure 3. Temperature-dependent turbidity measurements of statistical copolymers from CPOxa and MEtOxa (st CP1 and st CP2) in ester form (filled symbols) and in acid form at pH 5.6 (open symbols).

Table 4. Phase transitions temperatures of hydrolyzed CPOxa/CEtOxa statistic and block copolymers measured by turbidimetry at varied pH values.

Polymer	st CP1-H	st CP2-H	st CP3-H	bl CP1-H	bl CP2-H	bl CP3-H
Theor. ratio of MEtOxa/CPOxa	0.1	0.2	0.31	0.2	0.41	0.59
Exp.^a ratio of MEtOxa/CPOxa	0.1	0.19	0.27	0.24	0.43	0.86
pH 1: Ttr (°C)	29.4	28.3	28.5	31.6	28.7	26.1
pH 5.6: Ttr (°C)	54.5	n.tr.	n.tr.	53	n.tr.	n.tr.
pH 12: Ttr (°C)	57.2	n.tr.	n.tr.	n.tr.	n.tr.	n.tr.

^a Calculated from ¹H NMR signal integrals; n.tr. = no turbidity till 70 °C.

Figure 4. Temperature-dependent turbidity measurements of hydrolyzed statistical copolymer st CP1-H at different pH values.

Figure 5. Temperature-dependent turbidity measurements of hydrolyzed block copolymers at pH 5.6.

Scheme 1. General reaction scheme for the synthesis of statistical (st CP) and block copolymers (bl CP) from CPOxa and MEtOxa monomers using 1,4-dibromobutene as a bi-functional initiator.