Using AIBN as an initiator, the following free radical polymerization reaction was initiated:

<MultiModal>![PEG-CPADB and monomers A and B, with AIBN as the initiator and ethanol/water = 80:20 as the solvent, can react at 70 degrees Celsius for 12 hours to obtain PEG-b-P(DIPEMA-co-BzMA). The structure of PEG-CPADB is as follows: one end is terminated with S=C(C1=CC=CC=C1)SC(CCC(OCC[*:x1])=O)(C)C#N, the other end is terminated with methoxy, and the middle is polyethylene glycol with a degree of polymerization of 44. The structural unit can be represented as [*:x1]OCC[*:x2]. "[*:x1]" represents the connection point between the left end group and the left end of the polyethylene glycol segment; "[*:x2]" represents the connection point between the right end of the polyethylene glycol segment and the right end group methoxy. The structure of PEG-b-P(DIPEMA-co-BzMA) can be represented as a triblock copolymer: the leftmost end is S=C(C1=CC=CC=C1)S[*:x3]; the first structural unit is CC(C[*:x4])([*:x3])C(OCCN(C(C)C)C(C)C)=O, with a degree of polymerization of x; the second structural unit is CC(C[*:x5])([*:x4])C(OCC1=CC=CC=C1)=O, with a degree of polymerization of y; the third segment is a straight chain, not a copolymer, and can be represented as [*:x5][C@](CCC(OCC[*:x6])=O)(C)C#N; the fourth structural unit is [*:x6]OCC[*:x7], with a degree of polymerization of 44; the rightmost end is terminated with methoxy. "[*:x3]" represents the connection point between the left end group and the left end of the first segment; "[*:x4]" represents the connection point between the right end of the first segment and the left end of the second segment; "[*:x5]" represents the connection point between the right end of the second segment and the left end of the third segment; "[*:x6]" represents the connection point between the right end of the third segment and the left end of the fourth segment; "[*:x7]" represents the connection point between the right end of the fourth segment and the right end group methoxy.](/media/uploads/4f5ccbc7-458f-4a4f-af5e-7a06f96a1e32.jpg)</MultiModal>

The structure of $\mathrm{AIBN}$ is shown below:
<MultiModal>![CC(C#N)(C)/N=N/C(C#N)(C)C](/media/uploads/865f7b12-20b5-44c2-b9f6-1daec995d97d.png)</MultiModal>

For the sake of simplicity, the segment with a degree of polymerization of x is referred to as segment x, the segment with a degree of polymerization of y is referred to as segment y, and the segment with a degree of polymerization of 44 is referred to as segment z. In the chain initiation stage, $\mathrm{AIBN}$ decomposes and reacts with PEG-CPADB to generate compound $\bf{C}$ and radical $\bf{D}$. The polymerized PEG-b-P(DIPEMA-co-BzMA) does not exist as a monomer in the system, but immediately self-assembles to form vesicles. The vesicles can encapsulate drug molecules, and changing the pH of the system can achieve drug release.

Which of the following statements is correct:

1.  Compound $\bf{C}$ has 11 carbon atoms.

2.  Radical $\bf{D}$ contains sulfur atoms.

3.  In the $\mathrm{EtOH/H_2O}$ mixed solvent, segments x and z are exposed on the inside and outside of the vesicles, forming hydrogen bonds with water and ethanol, thereby encapsulating a certain amount of solvent molecules.

4.  To increase the rate of drug release from the vesicles, the degree of polymerization of segment x can be increased while keeping the degree of polymerization of other segments unchanged.

5.  To increase the rate of drug release from the vesicles, the degree of polymerization of segment y can be increased while keeping the degree of polymerization of other segments unchanged.

6.  To increase the rate of drug release from the vesicles, the degree of polymerization of segment z can be increased while keeping the degree of polymerization of other segments unchanged.

7.  To increase the pH value of the solution when the vesicles release the drug, the monomer of segment x can be replaced with DEAEMA (the structure is shown below).

<MultiModal>![CCN(CCOC(C(C)=C)=O)CC](/media/uploads/e1937d2c-0402-442e-b52b-d3ed52ea8b91.png)</MultiModal>
以 $\mathrm{AIBN}$ 为引发剂，引发了如下自由基聚合反应：

<MultiModal>![PEG-CPADB与单体A和单体B以AIBN作引发剂、以乙醇/水=80:20 作溶剂，在70度下反应12小时可以得到PEG-b-P(DIPEMA-co-BzMA)。其中PEG-CPADB的结构如下：一端以S=C(C1=CC=CC=C1)SC(CCC(OCC[*:x1])=O)(C)C#N封端，另一端以甲氧基封端，中间为聚合度为44的聚乙二醇，结构基元可以表示为[*:x1]OCC[*:x2]。“[*:x1]”表示左边端基与聚乙二醇片段左端的连接点；“[*:x2]”表示聚乙二醇片段右端与右侧端基甲氧基的连接点。PEG-b-P(DIPEMA-co-BzMA)的结构可以表示为三嵌段共聚物：最左端为S=C(C1=CC=CC=C1)S[*:x3]；第一段结构基元为CC(C[*:x4])([*:x3])C(OCCN(C(C)C)C(C)C)=O，聚合度为x；第二段结构基元为CC(C[*:x5])([*:x4])C(OCC1=CC=CC=C1)=O，聚合度为y；第三段为直链，非共聚物，可表示为[*:x5][C@](CCC(OCC[*:x6])=O)(C)C#N；第四段结构基元为[*:x6]OCC[*:x7]，聚合度为44；最右端以甲氧基封端。“[*:x3]”表示左边端基与第一段左端的连接点；“[*:x4]”表示第一段右端与第二段左端的连接点；“[*:x5]”表示第二段右端与第三段左端的连接点；“[*:x6]”表示第三段右端与第四段左端的连接点；“[*:x7]”表示第四段右端与右边端基甲氧基的连接点。](/media/uploads/4f5ccbc7-458f-4a4f-af5e-7a06f96a1e32.jpg)</MultiModal>

$\mathrm{AIBN}$的结构如下图：
<MultiModal>![CC(C#N)(C)/N=N/C(C#N)(C)C](/media/uploads/865f7b12-20b5-44c2-b9f6-1daec995d97d.png)</MultiModal>

为指代简便，将聚合度为x的片段称为片段x，将聚合度为y的片段称为片段y，将聚合度为44的片段称为片段z。在链引发阶段，$\mathrm{AIBN}$ 分解并与PEG-CPADB反应生成化合物 $\bf{C}$ 和自由基 $\bf{D}$。聚合形成的PEG-b-P(DIPEMA-co-BzMA)在体系中并非以单体存在，而是立刻自组装形成囊泡。囊泡可包载药物分子，改变体系的 pH，可实现药物的释放。

下列说法正确的是：

1.化合物 $\bf{C}$ 有11个碳原子。

2.自由基 $\bf{D}$ 中有硫原子。

3.在 $\mathrm{EtOH/H_2O}$ 混合溶剂中，片段x与片段z裸露在囊泡的内部和外部，与水和乙醇形成氢键，进而包裹一定量的溶剂分子。

4.为提高囊泡释放药物的速率，可以在其他片段聚合度不变的前提下，增加片段x的聚合度。

5.为提高囊泡释放药物的速率，可以在其他片段聚合度不变的前提下，增加片段y的聚合度。

6.为提高囊泡释放药物的速率，可以在其他片段聚合度不变的前提下，增加片段z的聚合度。

7.为提高囊泡释放药物时溶液的pH值，可以将片段x的单体换为DEAEMA（结构如下图所示）。

<MultiModal>![CCN(CCOC(C(C)=C)=O)CC](/media/uploads/e1937d2c-0402-442e-b52b-d3ed52ea8b91.png)</MultiModal>
2,3,4,6
1,4,7
2,3,4,7
3,4
2,6,7
1,4
1,7
1,6
1,2,3,4,7
1,3,4,7
All of the above options are incorrect or incomplete.
2,3,4,6
1,4,7
2,3,4,7
3,4
2,6,7
1,4
1,7
1,6
1,2,3,4,7
1,3,4,7
以上选项均错误或不完全。
Under heating conditions, compound $\mathrm{AIBN}$ can decompose to produce nitrogen gas and the free radical $\mathrm{·C(CH_3)_2(CN)}$, which can undergo an addition reaction with the most reactive carbon-sulfur double bond in PEG-CPADB, followed by elimination to obtain $\bf{C}$ and the cyano-stabilized tertiary carbon free radical $\bf{D}$. The structure of $\bf{C}$ is as follows:

<MultiModal>![S=C(C1=CC=CC=C1)SC(C)(C)C#N](/media/uploads/f280094e-6973-4aaa-871f-d1ce54b0ece4.png)</MultiModal>

Therefore, compound $\bf{C}$ has 11 carbon atoms.

<Checkpoint>[Compound $\bf{C}$ has 11 carbon atoms, option 1 is correct](1)</Checkpoint>

Free radical $\bf{D}$ does not contain a sulfur atom.

<Checkpoint>[Free radical $\bf{D}$ does not contain a sulfur atom, option 2 is incorrect](1)</Checkpoint>

The polymer has hydrophobic P(DIPEMA-co-BzMA) blocks (segment x and segment y) and a hydrophilic PEG block (segment z). In a mixed $\mathrm{EtOH/H_2O}$ solvent, the hydrophobic P(DIPEMA-co-BzMA) blocks self-assemble to form vesicles due to hydrophobic interactions; the hydrophilic PEG blocks are exposed on the inside and outside of the vesicles, forming hydrogen bonds with water and ethanol, thereby encapsulating a certain amount of solvent molecules.

<Checkpoint>[In a mixed $\mathrm{EtOH/H_2O}$ solvent, the hydrophilic segment z is exposed on the inside and outside of the vesicles, while segment x is a hydrophobic group, option 3 is incorrect](1)</Checkpoint>

Under acidic conditions, the diisopropylamino groups on the side chains of the P(DIPEMA-co-BzMA) block bind $\mathrm{H^+}$, which enhances the hydrophilicity of the chain segment, disrupting the vesicle structure and leading to drug release. Therefore, increasing the degree of polymerization of segment x can increase the number of sites that bind to hydrogen ions, thereby increasing the rate of drug release from the vesicles. Increasing the degree of polymerization of the hydrophobic segment y will decrease the rate of drug release from the vesicles. Increasing the degree of polymerization of segment z will also not increase the rate of drug release from the vesicles.

<Checkpoint>[To increase the rate of drug release from the vesicles, one can increase the degree of polymerization of segment x while keeping the degree of polymerization of other segments unchanged, rather than increasing the degree of polymerization of segments y and z. Option 4 is correct, options 5 and 6 are incorrect.](1)</Checkpoint>

Compared to the monomer of segment x, 2-(diisopropylamino)ethyl methacrylate, DEAEMA is also a tertiary amine with almost the same electronic effects, but DEAEMA has less steric hindrance, and the nitrogen atom is more easily bound to protons, so it is more basic.

<Checkpoint>[DEAEMA is more basic than the monomer of segment x.](1)</Checkpoint>

Replacing the monomer of segment x with DEAEMA allows proton binding and drug release from vesicles at a higher pH value, thus increasing the pH value of the solution during drug release from the vesicles.

<Checkpoint>[Replacing the monomer of segment x with DEAEMA can increase the pH value of the solution during drug release from the vesicles, option 7 is correct](1)</Checkpoint>

Therefore, the final answer is B.
在加热条件下，化合物 $\mathrm{AIBN}$ 可分解产生氮气以及自由基 $\mathrm{·C(CH_3)_2(CN)}$，可与PEG-CPADB中最活泼的双键碳硫双键发生加成反应，随后消除得到 $\bf{C}$ 和被氰基稳定的三级碳自由基 $\bf{D}$。$\bf{C}$ 结构如下：

<MultiModal>![S=C(C1=CC=CC=C1)SC(C)(C)C#N](/media/uploads/f280094e-6973-4aaa-871f-d1ce54b0ece4.png)</MultiModal>

因此，化合物 $\bf{C}$ 有11个碳原子。

<Checkpoint>[化合物 $\bf{C}$ 有11个碳原子，选项1正确](1)</Checkpoint>

自由基 $\bf{D}$ 中没有硫原子。

<Checkpoint>[自由基 $\bf{D}$ 中没有硫原子，选项2错误](1)</Checkpoint>

该聚合物具有疏水的P(DIPEMA-co-BzMA)嵌段（片段x和片段y）和亲水的PEG嵌段（片段z）。在 $\mathrm{EtOH/H_2O}$ 混合溶剂中，疏水的P(DIPEMA-co-BzMA)嵌段依靠疏水作用自组装形成囊泡；亲水的PEG嵌段裸露在囊泡的内部和外部，与水和乙醇形成氢键，进而包裹一定量的溶剂分子。

<Checkpoint>[在 $\mathrm{EtOH/H_2O}$ 混合溶剂中，亲水的片段z裸露在囊泡的内部和外部，而片段x为疏水基团，选项3错误](1)</Checkpoint>

在酸性条件下，嵌段P(DIPEMA-co-BzMA)侧链的二异丙基氨基结合 $\mathrm{H^+}$，使得链段的亲水性增强，囊泡结构被破坏，进而使得药物被释放出。因此，增加片段x的聚合度，可以增加与氢离子结合的位点数，进而增加了囊泡释放药物的速率。而增加疏水的片段y的聚合度会降低囊泡释放药物的速率。增加片段z的聚合度也不会增加囊泡释放药物的速率。

<Checkpoint>[为提高囊泡释放药物的速率，可以在其他片段聚合度不变的前提下，增加片段x的聚合度，而非增加片段y、片段z的聚合度。选项4正确，选项5、6错误。](1)</Checkpoint>

DEAEMA相比于片段x的单体2-(二异丙氨基)乙基甲基丙烯酸酯，同为三级胺，电子效应几乎相同，但DEAEMA的空间位阻更小，氮原子更易于与质子结合，因此碱性更强。

<Checkpoint>[DEAEMA相比于片段x的单体碱性更强。](1)</Checkpoint>

将片段x的单体换为DEAEMA后在更高pH值的溶液即能结合质子，使囊泡释放药物，因此可以提高囊泡释放药物时溶液的pH值。

<Checkpoint>[将片段x的单体换为DEAEMA可以提高囊泡释放药物时溶液的pH值，选项7正确](1)</Checkpoint>

因此最终答案为B。